A gene encoding Hordeum vulgare dehydration-responsive element binding protein 1 (HvDREB1), a member of the A-2 subgroup of the DREB subfamily, was isolated from barley seedlings. A subcellular localization assay revealed accumulation of HvDREB1 protein in the nucleus. As a trans-acting factor, HvDREB1 was able to bind to DRE/CRT elements and transactivate reporter gene expression in yeast cells. A study of various deletion mutants of HvDREB1 proteins indicated that the transactivation activity was localized to the N-terminal region. Expression of the HvDREB1 gene in barley leaves was significantly induced by salt, drought, and low-temperature. In contrast to most A-2 subgroup members in Arabidopsis thaliana, HvDREB1 also responded to exogenous ABA. Overexpression of HvDREB1 activated a downstream gene, RD29A, under normal growth conditions and led to increased tolerance to salt stress in Arabidopsis plants. These results suggest that HvDREB1 produces a DRE-/CRT-binding transcription factor that may have an important role in improving salt tolerance in plants.